The present invention relates to an electric generator system for being mounted on the output shaft of a gas turbine, and more particularly to an electric generator system for a gas turbine, which produces electric output power for driving wheels to propel a motor vehicle.
Gas turbines, which generate rotary mechanical output power based on combustion gases that are produced upon combustion of fuel and supplied at high temperature under high pressure, are mechanically simpler and easier to handle than steam turbines and reciprocating engines. Since gas turbines can produce large horsepower, can use low-quality fuel, and are less liable to break down and vibrate, they are used as prime movers for electric generators and ships.
In one application, a gas turbine is used as a prime mover for automobiles which are subject to a wide range of varying loads. More specifically, an electric generator is connected to the rotatable shaft of a gas turbine, and the electric output power generated by the generator is supplied to an electric motor mounted on the drive shaft of wheels, thus propelling the automobile.
It is not preferable for the rotational speed of the gas turbine to vary depending on changes in the load on the gas turbine. The electric generator connected to the gas turbine is therefore always supplied with the output power from the gas turbine as it rotates at high speed. Unless the size of the electric generator is large, it cannot drive the motor vehicle with good efficiency. If a smaller-size generator were used depending on the motor vehicle, it could not sufficiently absorb the output power from the turbine which rotates at high speed.
As shown in FIG. 2 of the accompanying drawings, when a turbine rotates at high speed, the effective efficiency of the output power of an electric generator which is coupled to the turbine becomes better as the load on the electric generator is higher, but lower as the electric generator is subject to a more partial load. Therefore, if a single electric generator is to cover a full range of loads, then such a system fails to increase the efficiency of the generator.